Ethers.js: Add floor and ceiling to FixedNumber

[thegostep]

[ricmoo]

An important reason why ethers has its own implementation of BigNumber is to be immutable.

So no in-place operations are available...

It makes things much simpler throughout the async nature of blockchain that capturing a reference is sufficient (also copying is fast; just store a reference) which requires all numbers remain immutable. Sorry. :s

[thegostep]

Is there an equivalent workaround with existing methods?

[ricmoo]

Well, you can just re-assign to the original value. :)

// equivalent to value.idiv(divisor)
value = value.div(divisor);

[thegostep]

Ah - okay sorry, I was not referring to inplace division, I was referring to integer division: https://mikemcl.github.io/bignumber.js/#divInt

[ricmoo]

Oh, I see. That makes more sense. :)

The BigNumber class will likely never support that, however, you can use the FixedNumber class to get something similar:

x = FixedNumber.from("5");
y = FixedNumber.from("0.7");

quotient = x.divUnsafe(y));
// "7.142857142857142857"

quotient.round()
// "7.0"

You can also specify the internal fixed format to use, which is by default fixed128x18 (i.e. 128 bits wide, representing 18 decimals).

Does that help?

[thegostep]

bare with me - I am a math noob

Is is possible to have a way for specifying if division rounds up or down?

[ricmoo]

Oh! That is actually something I’ve been meaning to add, but it hasn’t been a priority. But I can add it this week.

I plan to support a bunch of tie-breaking rounding algorithms:

• round half up (this is what round currently does)
• round up (ceiling)
• round down (floor)
• round toward zero
• round away from zero
• round to odd
• round to even

For now I will add floor and ceiling. If there is any other rounding strategy you need though, let me know.

[ricmoo]

I've added a .floor and .ceiling method to BigNumber in 5.0.13. Try it out and let me know if it works for you.

Thanks! :)

[ricmoo]

This has been published, so I'm going to close it now. If you have any issues though, please re-open.

Thanks! :)

[thegostep]

I've been trying to convert this function into using only ethers BigNumber - any tips?